This invention relates generally to machinery for removal of material from logs and more particularly to high speed log debarkers.
Debarkers are widely used in the forest products industry to remove bark from logs intended for many uses, including sawing into lumber, peeling for veneer, poles and posts, and for chipping. Most such apparatus are arranged to receive a whole log and to debark the entire length of the log in a single, parallel-type operation, essentially by rotating the log about its lengthwise axis in contact with a series of cutting elements disposed lengthwise along the log. Examples of this type of apparatus are shown in U.S. Pat. Nos. 2,498,786; 2,698,036; 2,611,401; 2,702,570; 3,267,976 and 4,444,234. This type of machine requires a very wide bed with many cutting elements to debark long logs. Alternatively, the logs must be limited in length. In either case, the debarking apparatus is very expensive and not readily portable.
The other type of debarker is arranged to feed a log lengthwise along a cutting element while rotating the log about its lengthwise axis, such as MORBARK Models 628 and 640. This type of debarker is less complex, not as expensive and log length is not a constraint as in the parallel-type debarkers referred to above. Its main drawback is that it is much slower. Examples of this type of debarker are disclosed in U.S. Pat. Nos. 1,373,243 and 4,540,031. A related type is the ring debarker, such as Nicholson Model A5 and Manitowoc Model 2202, which peels off the bark in a spiral fashion as the cutter head moves lengthwise along the log. Another type is the flail-type debarker, such as the Peterson Pacific Models 4800 and 5200, in which the log is moved lengthwise past two or four drums carrying whirling chains which flail the bark off a log.
As old growth forests no longer are available, and for economic reasons, it is becoming increasingly important to be able to use smaller diameter timber for many forest products applications. The main problem that results is that the yield of useful wood from smaller logs is less than in larger logs. It becomes necessary to cut and debark more smaller diameter trees to produce, for example, a given mass of wood chips than required for large diameter logs. Throughput of a debarker thus becomes a critical requirement.
At the same time, to reduce travel in hauling harvested logs to a debarker, it is preferable to be able to locate the debarker nearer the tree source and be able to move it when harvesting a distant stand of trees. The higher throughput ring-type debarkers are generally too big and complex to be readily disassembled and moved, and are too expensive to have many of them at dispersed locations. The latter, lengthwise-infeed type of debarker mentioned above is less expensive and more portable but not nearly as fast at debarking, so throughput for small-diameter logs is unsatisfactory.
Another concern, whichever type of debarker is used, is to be able to handle a wide range of log diameters. Conventional ring-type debarkers, commonly used in fixed installations in mills, are made to handle logs ranging in diameter from a maximum of 35 inches (90 cm.) down to 6 inches (15 cm.). They cannot debark smaller but usable logs or log ends which taper down to 3 inches (8 cm.) or less in diameter at their narrower end. These narrow logs must somehow be disposed of or discarded, presenting environmental concerns as well as wasting a substantial mass of fiber that would otherwise be useful at least as chips for pulp. A flail-type debarker, which can be portable, will handle a wide range of diameters but breaks up the smaller diameter ends, particularly if the wood is dry, again wasting much useful fiber. All available debarkers are very expensive--too much for low-value, small diameter logs that are not large enough to use as saw logs.
Accordingly, a need remains for a debarker that is more versatile, portable, and capable of high throughput but not prohibitively expensive.